Throughout the world, various liquids and gases are stored in bulk amounts in storage tanks or containers. Many of the liquids or gases are dangerous because they are flammable, poisonous, corrosive, and/or carcinogenic. Many of these storage tanks are installed underground and are subject to naturally occurring corrosive agents and shifting ground. In the past, many of the underground tanks became damaged by virtue of corrosion, shifting ground, inadvertent drilling or puncturing from nearby construction. Of course, a damaged tank can leak pollutants into the environment. Above ground storage tanks may also develop leaks; however, leaks in underground storage tanks are difficult to detect. Initially, these leaks can occur slowly and go undetected for many years. Even if detected, in the past many owners of underground tanks did not repair the tanks if the leaks were small relative to repair costs.
A majority of the underground storage tanks are used for the storage of gasoline at retail stations. Most of these retail gas stations are located in highly populated areas and thus the health hazard is obvious. Typically, underground storage tanks are constructed of metal or fiberglass reinforced resinous materials. Historically, these underground tanks were not installed with outer containment tanks. Therefore, many of the older tanks (especially steel tanks) are or may become damaged and leak pollutants into the environment.
Due to the potential public health hazards described above, new federal regulations and local ordinances have been enacted or are presently being proposed to require the owners of underground storage tanks to repair and/or replace damaged tanks which leak. The regulatory movement is also directed at requiring that more leak resistance storage tanks be initially installed.
The approach adopted by most manufacturers to improve the containment of liquids in underground storage involve the use of a double wall constructed storage tank. For example, such tanks are disclosed in U.S. Pat. Nos. 4,708,015; 4,685,327; 3,848,765; and 4,568,925. Some of these storage vessels, as disclosed in the patents, also have a leak detecting system of some type. The difficulty with the double wall construction is that the fabrication is complicated, care must taken in fabricating the outer tank such that the inner tank is not damaged. Many have a fiberglass outer shell which can be cracked or punctured in shipment. If the flaw is not detected prior to installation the outer shell will not serve any containment function. In these vessels, if a leak does occur and is detected, the only solution is to dig up the tank and replace the assembly in toto, or attempt to repair the inner vessel from the inside. Such repairs require draining the tank, assuring that it is safe enough for workmen to enter, and creates difficulties in being able to assure that repairs to the inside tank do not damage the outer tank. Furthermore, these double tanks are fairly rigid, and in areas of the country where earthquakes are a potential hazard, the tank may be fractured as a result of pressure exerted by an earthquake. Thus, there is a need to provide an economical, easily manufactured, versatile and reliable containment system for storage of material and, in particular the underground storage of materials.
The present invention provides for a containment system which provides for an outer containment vessel which is inexpensive to construct, easily assembled, utilizes conventional single walled storage containers such as tanks or drums, and provides for easy repair and replacement of the storage container without damage to the outer containment vessel.